As rising crime propels one Baltimore neighborhood after another to consider paying for private police protection, the local practice begins to mirror a national trend that law enforcement experts describe as inevitable.

In Los Angeles, in Dallas, in Detroit -- wherever there isn't enough protection to satisfy taxpayers -- some residents will manage to acquire protection of their own, law enforcement experts say.

"There's no question that it's a trend," says Robert Trojanowicz, director of the Michigan-based National Center for Community Policing and a critic of the privatization of police services. "In the short term, private security makes people feel better. In the long term, it raises some questions."

Baltimore's upper- and middle-class neighborhoods are behind the national curve. In crime-battered Detroit, middle-income communities like Palmer Park and Lafayette Park have hired private security guards to augment the regular city patrols. In Dallas, a coalition of community groups have joined to do the same thing. Depending on the number of participants, the costs for each residence can range from $200 to $2,000 a year.

In Los Angeles -- where the city Police Department is perhaps the most undermanned in the country -- hundreds of private security guards are employed to protect everything from the isolated hillside canyon homes, to exclusive neighborhoods such as Bel Air, to middle-class communities in the San Fernando Valley.

"With the number of police in L.A. and the way the city's laid out, they've got to have private security in some of those areas," says Charles E. Dennis Jr., executive director of the World Association of Detectives, an international organization for private investigators and security groups. "If they didn't, the response time to a crime would be ridiculous."

Locally, only a portion of the affluent Guilford community in North Baltimore has actually hired off-duty police to provide neighborhood patrols, but news of that program, which began in September, has spread rapidly. Guilford residents say they have already spoken with five more interested neighborhood groups.

"We're going full steam ahead," says Brooks Bosley, of the Mount Royal Improvement Association, which has met with Guilford residents to learn about establishing a private security program in Bolton Hill. Tentatively, residents of the area will be asked to pay $520 a year.

"Right now, we're trying to determine just how many residents will participate, and given that number, how much of a contribution will be required," Mr. Bosley said.

Roland Park is also considering such a program, as are West Baltimore's Hunting Ridge community and two Baltimore County neighborhoods.

Meanwhile, business owners in the Mount Vernon-Belvedere area and the 25th Street corridor are talking about creating a special taxing district that would provide security and cleanup crews. Those efforts would be similar to those of the Downtown Partnership of Baltimore, a quasi-public group providing the same services to the downtown business district.

City officials say they generally support grass-roots efforts to improve security. "If any community has a legitimate desire to have improved police response, then the position of the city and the Police Department is to assist them as much as possible," says Mayor Kurt L. Schmoke.

In light of the City Council's recent unwillingness to hire more officers by increasing taxes, Mr. Schmoke says he still hopes to find funds -- perhaps from the new Clinton administration -- to increase police services in Baltimore.

While he supports the private patrols, the mayor acknowledges some concern that moonlighting among city officers could increase markedly. "I do worry that at some point there will be a tilt in the balance, and officers will be giving more of their energies to overtime details than to public duties," he says.

Currently, Baltimore police officers are permitted to seek secondary employment -- a "safety valve" benefit that allows them to live on salaries that often aren't competitive with those of other law enforcement agencies. Overtime details must be approved by the police commissioner on a case-by-case basis.

The security industry itself has long been concerned about the same trend, albeit for different reasons. For more than a decade, industry officials have complained that the use of off-duty officers for private security is unfair competition -- especially when moonlighting officers have use of departmental vehicles, uniforms and other equipment.

But Guilford residents and others say using off-duty city officers for the private patrols assures greater professionalism and less risk of civil liability.

Nationally, a persistent criticism of private firms involves the reliability of their guards and officers, who -- even when armed -- have no legal authority beyond that of an ordinary citizen in most instances.